Pediatric brain tumors are the most common malignant solid tumors in children. Despite modern treatments having increased survival, current therapeutics often carry debilitating side effects with them, including lifelong intellectul and neurological disability. Because of this, there is a pressing need for novel therapeutic approaches. While transforming growth factor-beta (TGF-) is one of the most well-studied immune molecules in cancer biology, in regards to pediatric brain cancer, precious little is known. We recently showed that genetic blockade of T cell TGF- signaling promotes CD8 cytotoxic T lymphocyte (CTL)-mediated anti-tumor immunity in the smoothened (SmoA1) mouse model of medulloblastoma (MB). Furthermore, inhibiting T cell TGF- signaling led to generation of CD8+ short-lived effector T cells (SLECs) that were efficient tumor cell serial killers. These results uncover a cellular immune mechanism whereby TGF- signaling blockade licenses CD8 SLEC-CTLs to kill pediatric brain tumors. The central theme of this revised exploratory grant application is to develop an experimental pharmacological approach for the treatment of MB. Specifically, we seek to test whether nanoparticle-based blockade of TGF- signaling in the key cellular mediator of anti- tumor immunity, the CD8 T cell, is a viable MB therapeutic approach. To achieve this goal, we will: 1) test whether CD8 targeted nanoparticle inhibition of TGF- signaling in peripheral T cells will prevent or treat established MB in SmoA1 mice, and 2) elucidate the mechanism of CD8 SLEC-CTL activity in nanoparticle-treated CD8 T cells. Through a collaborative effort, we have already developed CD8- targeted nanoparticles consisting of the biodegradable polyester, poly(ethylene glycol) and poly(lactic-co-glycolic) acid (PEG-PLGA), encapsulating the small molecule TGF--Smad 2/3 signaling inhibitor (SB-505124) and the non-toxic fluorescent tracer, Coumarin-6 (C6). In Specific Aim 1, we will utilize this pharmacologically-relevant method to target TGF- signaling in CD8 T cells in SmoA1 mice. Both disease prevention and active treatment study arms will be carried out. For Specific Aim 2, CD8 T cells will be isolated from SmoA1 animals treated with C6 or C6/SB nanoparticles and tumor cell killing will be read-out by an established CTL assay. Western blot analysis will be performed on isolated CD8 T cells from these animals to verify TGF- signaling inhibition. Immunophenotyping will be carried out to determine if CD8 T cell TGF- signaling blockade promotes conversion to SLEC-CTLs. We hypothesize that nanoparticle-mediated TGF- pathway blockade in CD8 T cells will prolong survival in a pre-clinical animal model of pediatric brain cancer by promoting the SLEC-CTL anti-tumor immune response.